Chromosomal abnormalities in embryos.

Chromosomal analysis was performed on 1620 embryos generated in vitro by patients with a poor prognosis of pregnancy. A diagnosis was yielded in 1596 embryos: 536 (34%) were euploid and 1060 (66%) carried chromosomal abnormalities. The results revealed a strong association between chromosomal abnormalities, cellular stage and percentage of fragmentation. In addition, 92% of embryos with multinucleated cells were diagnosed mosaics, whereas the presence of cytoplasmic concentration was associated to 86% chromosomal abnormalities. The rate of development to expanded blastocysts was dependent on both the cleavage stage at the time of blastomere biopsy and the chromosomal status of the embryos. The highest percentage of blastocyst growth derived from embryos with 7-8 cells on the morning of day 3: 68% were generated from euploid embryos and 43% from chromosomally abnormal embryos. These findings suggest that morphological criteria alone are not sufficient in poor prognosis patients to guarantee the best embryo selection.